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Scaling Petroleum Migration Using Oil Tracers: Models and Experiments to Assess the Oil Migration Timing and Distance

Abstract

Understanding the timing and distance of crude oil migration through the subsurface from source kitchen to reservoir accumulations is important for predicting the location and volumes of other potential hydrocarbon accumulations within an oilfield. These migration characteristics may be determined by modeling the evolution of a set of oil tracers along the migration pathway. We present a numeric model based on a set of oil tracers that is designed to calculate the migration distance and timing for the oil flowing from the source to the reservoir accumulation. The oil tracers used as molecular markers were nitrogen-based aromatic compounds such as carbazole and its derivatives naturally generated along with crude oil. They have the property to continuously changing their absolute and relative composition along a migration pathway due to various processes modeled. The model starts with an initial concentration of tracers resulted from the oil generation process and calculates the distribution in space and time of tracer concentrations. The distribution is then converted to migration distance. To calibrate the model, an initial concentration of the oil tracers is considered based on the thermal evolution of the source rock and laboratory experiments to determine the kinetic parameters of the source rock transformation with respect to each tracer component. A number of 9 hydrous-pyrolysis experiments were performed on immature type-II kerogen with temperatures ranging from 290-360°C for 72 hours to simulate petroleum generation. Generated oil samples from hydrous-pyrolysis reactor were collected, and carbazoles compounds concentrations were measured using gas chromatography - mass spectrometry (GC-MS) technique. The measurements helped to derive Arrhenius parameters (i.e. activation energy (Ea) and frequency factor (A). To test our model, we used it to estimate the potential for oil accumulation in a reservoir structure within a partially developed field. Using the calculated migration distance and timing, we determined the filling sequence of accumulations. The concentration of multiple tracer components from well samples of the known accumulations were used to calibrate the model. The tracer model offers a method to calibrate basin simulations and map-based analyses for the migration distance and timing when tracer measurements are available anywhere within the basin being explored.